concatenation with a row between

Try this to see if you get the desired output.

Sub vimalanathk()
Dim rng, cell As Range
Dim lr As Long
lr = Cells(Rows.Count, 1).End(xlUp).Row
Set rng = Range("A1:A" & lr)
Application.ScreenUpdating = False
For Each cell In rng
    cell.Select
    If cell <> "" And IsNumeric(Left(cell.Offset(1, 0), 1)) Then
        cell = cell & " " & cell.Offset(1, 0)
        cell.Offset(1, 0).ClearContents
    End If
Next cell
Application.ScreenUpdating = True
End Sub

Please find the attached sheet and click on the Green Button to get the desired output.

See the attached sheet.